Changes:
- Note.kt: Add checklistSortOption field (String?, nullable for backward compatibility)
- Note.fromJson(): Parse checklistSortOption from JSON
- Note.fromMarkdown(): Parse sort field from YAML frontmatter
- Note.toMarkdown(): Include sort field in YAML frontmatter for checklists
- ChecklistPreviewHelper.kt: New file with sortChecklistItemsForPreview() and generateChecklistPreview()
- NoteEditorViewModel.loadNote(): Load and restore checklistSortOption from note
- NoteEditorViewModel.saveNote(): Persist checklistSortOption when saving (both new and existing notes)
- NoteCardCompact.kt: Use generateChecklistPreview() for sorted preview (includes IMPL_06 emoji change)
- NoteCardGrid.kt: Use generateChecklistPreview() for sorted preview (includes IMPL_06 emoji change)
2c43b47e96